1. Field of the Invention
The present invention relates to a miniaturized device for connecting electrically conducting elements subjected to very high currents.
Electrically conducting elements are generally connected by bringing together two conductors subjected to a pressure created by a mechanical system. These conductors are very generally made from copper more rarely from brass or silver. Since these metals are very good conductors of electricity the dimensions of the connecting wires are very small even for very high currents. For example, a hundred amps or so may be carried by a copper wire of a section of 0.1 mm.sup.2 without melting. On the other hand, the connection of such elements involves much greater dimensions of the conductors. In contact with the conductors, the resistivity is very high. That is due to oxides, to surface impurities, to the reduction of the contact area. To obtain a good connection despite this high resistivity, the connecting area is increased and of course the space required as well. These considerations lead to very large dimensions for the connection with respect to the dimensions of the conductor itself. In the case of clamping by screws and binding clips, over identical lengths, the space occupied by the connection is 30 to 100 times greater than the space occupied by the conductors.
A method of making the connection very small would be to form an autogenous weld. Now, copper does not lend itself very well to this type of welding because it is a good conductor of electricity. End welding is not 100% reliable for the production of heat is caused by the oxide on oxide connection and they remain in the weld. A laser gives no result on copper for the very pin-point heat is discharged too rapidly. Ultrasonic welding gives a satisfactory result but only for large section connections for die-stamping is required. Silver brazing is excluded because of the high temperatures required for too long a time, which is not suitable for electronic components.
2. Description of the Prior Art
A known solution for reducing the dimensions of the connection consists in forming the connection by means a of low melting point and electrically conducting binder. For easy use of this binder, fusion of the binder is used. At ambient temperature, this latter is solid and provides the mechanical connection and the electric continuity between the two conductors while holding them adjacent one another over a certain length which is embedded in an elongate welding block. This binder, generally made from a lead-tin alloy, is inevitably a less good conductor of electricity than copper, so of inferior quality and the connecting length must be very great for the very high currents so as to avoid melting of the binder; the ratio of the spaces occupied remains from 10 to 100 times greater, i.e. the volume of the final connection is from 10 to 100 times greater than the volume of the portions adjacent the two wires. The melting point of the binder is relatively low between 200.degree. and 300.degree. C., so as to facilitate use thereof and so as not to impair the environment (fixing elements, chips, insulators, electronic components sensitive to the heat).
A device is moreover known, as described in the patent No. GB-A-1 465 662, for providing a connection between a bar and a conducting element, usable more particularly in electrometallurgy, this device comprising, between the bar and the conducting element, a mass of an electrically conducting fluid material kept confined by a skirt made from a flexible material, so as to allow relative movement. Such a device however does not solve the problem of connecting copper or another good electrically conducting material, of small dimensions (a few millimeters) subject to very high currents (50 kA to 100 kA).
The result is that no solution known at present allows the connections to be miniaturized in a ratio of 2 to 3, instead of 10 to 100. for very high currents, while keeping very great operating or connection reliability. Such reliability of connection at very high currents is not usually necessary in electric appliances, for these very high currents are produced by fault currents. If the connection is interrupted by melting of the binder for example, that interrupts at the same time the fault current and so the reliability is increased thereby. The same cannot be said for lightning or overvoltage protectors through which very high currents flow to ground. The operating reliability requires that the connection be never interrupted even for the very high currents generated by lightning (100,000 amps). If the flow to ground were interrupted by a break in the connection, an overvoltage would appear at the terminals of the device and the overvoltage protective device would no longer serve any purpose.
The present invention aims at overcoming these drawbacks by providing a connection device of particularly simple design allowing very high miniaturization while providing 100% operating reliability in an application to a miniaturized overvoltage or lightning protector device.